Hellish Venus may have lost its water quickly
By JONATHAN O’CALLAGHAN, Science.
Excerpt: With surface temperatures hot enough to melt lead, Venus today is a veritable hellhole, despite being similar in size to Earth and orbiting in the habitable zone of the Sun. Yet studies suggest the planet may have once hosted oceans and even conditions suitable for life. Explaining how all that water disappeared has been a problem. A study published today in Nature offers a solution, identifying a new water-loss mechanism operating high in Venus’s atmosphere that could have doubled the rate of water loss. Speedier drying could have allowed oceans to exist until later in Venus’s history—implying the planet might have been habitable for longer. ...At 96% carbon dioxide, its atmosphere traps so much heat that surface temperatures reach more than 450°C. Yet spacecraft and telescopes have seen faint hints of water vapor in the atmosphere, and in the late 1970s, NASA’s Pioneer Venus orbiter detected a sign of long-vanished oceans: an enrichment of heavy hydrogen, deuterium. ...The authors of the new study say they have identified new water-loss chemistry that can resolve the problem. ...some 150 kilometers above the surface, sunlight would not only split water vapor but also carbon dioxide, creating hydrogen and carbon monoxide that would combine into an unstable ion called HCO+ ...[that] would break apart to shed excess energy. ...“The hydrogen uses the carbon monoxide molecule as a launchpad to escape to space,” explaining how the last “dregs” of venusian water could have been lost even after hydrodynamic loss ceased. ...Venus may have held onto its oceans until much more recently, perhaps 2 billion to 3 billion years ago....